1. Field of the Invention
The present invention relates to a memory designation control device used in a printer system or the like.
2. Description of the Prior Art
In recent years, in printer systems and the like, a basic program has been stored in a rewritable ROM (Read Only Memory) such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash EEPROM (Flash Electrically Erasable Programmable Read Only Memory), and the basic program has been rewritten without replacing the memory devices. The basic program is typically rewritten on the basis of a rewriting program other than the basic program.
An attempt to store the rewriting program in the same rewritable ROM storing the basic program and then rewriting the basic program with the rewriting program causes not only the basic program but also the rewriting program to be rewritten, so that the program is corrupted. Furthermore, in the flash EEPROM, in rewriting the contents thereof, all the contents are erased at the same time. Accordingly, the rewriting program is stored in a memory device such as an EPROM (Erasable Programmable Read Only Memory) different from the rewritable ROM storing the basic program. Addresses different from those assigned to the rewritable ROM storing the basic program are assigned to the memory device storing the rewriting program.
In the above described conventional system, if the power supply is turned off while the basic program stored in the rewritable ROM is being rewritten, processing based on an incomplete basic program which is rewritten only halfway is started next time the power supply is turned on. Therefore, the system does not operate normally.
An object of the present invention is to provide a memory designation control device capable of normally operating a system, even if the power supply is turned off while the contents of a rewritable ROM are being rewritten, when the system is subsequently operated.